Hemodilution Combined With Hypercapnia Impairs Cerebral Autoregulation During Normothermic Cardiopulmonary Bypass

Objective To investigate the influence of hemodilution and arterial pCO 2 on cerebral autoregulation and cerebral vascular CO 2 reactivity. Design Prospective interventional study. Setting University hospital-based single-center study. Participants Forty adult patients undergoing elective cardiac surgery using normothermic cardiopulmonary bypass. Interventions Blood pressure variations induced by 6/minute metronome-triggered breathing (baseline) and cyclic 6/min changes of indexed pump flow at 3 levels of arterial pCO 2 . Measurements and Main Results Based on median hematocrit on bypass, patients were assigned to either a group of a hematocrit≥28% or 2 reactivity was calculated using cerebral tissue oximetry data. Cerebral autoregulation as reflected by autoregulation index (baseline 7.5) was significantly affected by arterial pCO 2 (median autoregulation index amounted to 5.7, 4.8, and 2.8 for arterial pCO 2 of 4.0, 5.3, and 6.6 kPa, p≤0.002) respectively. Hemodilution resulted in a decreased autoregulation index; however, during hypocapnia and normocapnia, there were no significant differences between the two hematocrit groups. Moreover, the autoregulation index was lowest during hypercapnia when hematocrit was 2 reactivity during hypocapnia was significantly lower when perioperative hematocrit was Conclusions Hemodilution down to a hematocrit of a CO 2 during CPB.